1. Field of the Invention
Aspects of the present invention relate to a lithium ion secondary battery, and more particularly, to a lithium ion secondary battery in which a separate battery part is coupled to an upper or first part of a cap plate of a bare cell.
2. Description of the Related Art
In general, primary batteries are not rechargeable, and secondary batteries are rechargeable. In recent years, for example, nickel-metal hydride (Ni-MH) batteries, lithium (Li) batteries, and lithium ion (Li-ion) batteries have been mainly used as the secondary batteries.
The lithium ion batteries are manufactured in various shapes. For example, the shapes of the lithium ion batteries may be classified into cylindrical, square prismatic, or pouch shapes according to the type of case used in manufacturing.
In the lithium ion battery, a carbon-based electrode is generally used as a cathode in order to reduce the risk of combustion or explosion. However, special emphasis is placed on the safety of the lithium ion battery in the manufacturing process due to the high energy density of lithium and the possibility of combustion reactions occurring with a non-aqueous electrolyte.
In order to improve the safety, the lithium ion battery generally includes a bare cell having a basic structure for charge or discharge and a protective circuit or a protective device for preventing overcharge, overdischarge, overheating, and overcurrent. The protective circuit or the protective device may be physically and electrically connected to the bare cell in the form of a printed circuit board and may be displaced on the side, the upper surface, or the lower surface of the bare cell.
In the cylindrical can battery, a cap assembly of a bare cell serves to prevent overheating and overcurrent. However, in the prismatic can battery, a cap assembly does not have such a safety feature. Therefore, in the prismatic can battery, particularly, a separate safety device should be coupled to the bare cell. In recent years, in many cases, the safety device of the prismatic can battery, such as a protective circuit board, is coupled to the upper surface of a cap plate.
Meanwhile, in a pack battery having a plurality of bare cells connected to one another, a battery part, such as a cap cover, may be coupled to an upper part of a cap plate in order for series/parallel connection of the bare cells in the pack or connection between the bare cells and a protective circuit.
An example of the cap cover will be described below. A peripheral portion or a body of the cap cover is generally formed of an insulating resin material, and forms a coupling part that is supported by a cap assembly of a bare cell while physically contacting the bare cell. A metal plate terminal that has a relatively narrow width and is connected to an electrode terminal of the bare cell is formed at the center of the lower surface of the cap cover. The narrow metal plate terminal is exposed through a hole formed in the center of the body of the cap cover. A wide metal plate terminal connected to a protective circuit terminal outside the bare cell may be provided in the vicinity of the hole on the upper surface of the cap cover. In addition, a conductive connecting part for connecting these metal plate terminals is provided.
However, in the cap assembly at the upper part of the bare cell, an electrode terminal protrudes from the surface of the cap plate and is insulated therefrom. Therefore, it is difficult to stably couple a battery part, such as a cap cover, to an upper part of the cap assembly. Further, it is difficult to stably couple the battery part to the bare cell by, for example, welding.
As a member for guiding the battery part to an accurate position with respect to the cell is not formed in the peripheral portion of the cap assembly, it is difficult to accurately couple the battery part to the upper part of the cap assembly. When the battery part is not accurately coupled to the cap assembly, it is difficult to achieve stable electrical connection between the battery part and the bare cell, which may cause defects in the electrical connection.
For example, when the cap cover is used for a pack battery, the cap cover should be fixed to the upper part of the cap plate. However, it is difficult to easily fix the cap cover to the cap plate, which may frustrate the manufacture of the pack battery.